There is known a vehicle luminaire having a socket and a light-emitting module provided in one end side of the socket. The light-emitting module has a board provided with a wiring pattern and a light-emitting diode (LED) electrically connected to the wiring pattern.
In order to light the vehicle luminaire, a voltage is applied to the vehicle luminaire (light-emitting module). As a voltage is applied to the light-emitting module, a current flows to the light-emitting diode, so that heat is generated, and a temperature of the light-emitting diode increases. Here, when a vehicle luminaire provided in an automobile, the voltage applied to the vehicle luminaire fluctuates. For this reason, an overvoltage significantly increases the temperature of the light-emitting diode, so that a failure may occur in the light-emitting diode, or a service life of the light-emitting diode may be reduced.
In this regard, a technique is proposed, in which a circuit obtained by connecting a resistance and a thermistor (positive temperature coefficient thermistor) in series and a resistance are connected in parallel, so that the thermistor cuts off the current in the event of an overvoltage to allow the current to flow only to the resistance connected in parallel. As a result, in the event of an overvoltage, a value of the resistance connected in series to the light-emitting diode increases. Therefore, it is possible to suppress the temperature of the light-emitting diode from excessively increasing.
Meanwhile, if the number or specification of the light-emitting diode changes, or a distance between the light-emitting diode and the thermistor changes, the temperature of the thermistor changes. For this reason, it is necessary to select a thermistor having a suitable Curie point and a suitable resistance value depending on the specification, size, use purpose, or the like of the vehicle luminaire.
However, if the thermistor is selected depending on the specification of the vehicle luminaire or the like, it is necessary to stock a plurality of types of thermistors. In addition, it may be difficult to find a thermistor having an optimum Curie point and an optimum resistance value, and the thermistor may not operate at a desired temperature in some cases.
In this regard, development of a technology capable of controlling the temperature of the control element such as a thermistor is demanded.